1. Field of the Invention
The present invention relates to a piezoelectric thin film element and a piezoelectric thin film device, using a piezoelectric thin film of alkali-niobium oxide series.
2. Description of the Related Art
A piezoelectric ceramics is processed into various piezoelectric elements in accordance with various purposes, and is widely used particularly as a functional electronic component such as an actuator for generating deformation by adding a voltage to the piezoelectric elements, and a sensor for detecting the voltage generated by deformation of the piezoelectric elements. As the piezoelectric ceramics used for the purpose of use of the actuator and the sensor, a dielectric material, being a lead-based material, having excellent piezoelectric properties, and particularly a PZT-based perovskite-type ferroelectric ceramics expressed by a composition formula: Pb(Zr1-xTix)O3 is widely known heretofore. PZT-based piezoelectric ceramics is ordinarily formed by sintering an oxide of each of the elements. With a progress of miniaturization and high performance of each kind of electronic component, the miniaturization and high performance of the piezoelectric elements are also strongly requested.
However, in a piezoelectric material fabricated by a sintering method, being a conventional method, as a thickness thereof becomes smaller, particularly as the thickness becomes nearly about 10 μm, a thickness of the piezoelectric thin film corresponds to almost a size of each crystal grain constituting the thin film, and an influence on the piezoelectric properties, etc, can not be ignored. Therefore, there is a problem that variation or deterioration of properties is remarkable. Therefore, in order to prevent such a problem, a forming method of the piezoelectric ceramics using a thin film technique instead of the sintering method, has been studied in recent years. Recently, a PZT thin film formed on a silicon substrate by sputtering has been put to practical use as a piezoelectric thin film of an actuator for an ink jet printer head with high-speed and high-definition (for example, see patent document 1).
Meanwhile, a piezoelectric sintered ceramics or a piezoelectric thin film made of PZT contains lead by about 60 to 70 wt %, and therefore is not preferable in terms of an ecological viewpoint and pollution control. Therefore, in consideration of an environment, development of the piezoelectric materials not containing lead is desired. At present, various lead-free piezoelectric materials are studied, including potassium sodium niobate (also described as “KNN” hereafter) expressed by a composition formula (K1-xNax)NbO3(0<x<1), composed of K (potassium), Na (sodium), Nb (niobium), and O (oxygen). The KNN is a material having a perovskite structure and shows relatively excellent piezoelectric properties for a lead-free material, and therefore is expected as a strong candidate of a lead-free piezoelectric material (for example, see patent document 2).